In a wheel loader or other work vehicle, a travel device and hydraulic pump are driven by a drive force from an engine. Driving of the travel device causes the vehicle to travel. Driving the hydraulic pump causes hydraulic fluid to be fed from the hydraulic pump to the work implement. The work implement is thereby driven.
There are also work vehicles comprising a torque converter device having a torque converter and a lockup clutch. The torque converter device transmits the drive force from the engine to the travel device via the torque converter when the lockup clutch is in a non-connected state (this state is hereinafter referred to as “torque conversion travel”). When the lockup clutch is in a connected state, the torque converter device transmits the drive force from the engine to the travel device via the lockup clutch (this state is hereinafter referred to as “lockup travel”). Switching the lockup clutch between the connected state and the non-connected state is automatically carried out by a controller. The controller switches the lockup clutch between the connected state and the non-connected state in accordance with the travel state of the vehicle. For example, the controller switches the lockup clutch from the non-connected state to the connected state when the vehicle speed reaches a predetermined switch speed (see Japanese Laid-open Patent Application No. 2009-103258).